| As a newly developed welding material accompanied with SMT, solder paste plays a predominant role in the reliability of solder interconnection. The quality of the solder paste depends on the performance of solder powder and flux. Based on Sn-3.0Ag-0.5Cu lead-free solder, solder powder was prepared by gas-atomization, effects of rare earth cerium on the microstructure and IMC growth behavior of solder joint were studied, the printing performance of solder paste and the formation law of voids in sold joint were also discussed.The micro structure of solder alloy and solder joint were observed by Metallographic Microscope and Scanning Electricity Microscope (SEM), the phase composition of solder alloy and solder joint was analyzed by Energy Dispersive Spectrometer (EDS). The oxygen content of solder power was measured by THC600Hydrogen/Nitrogen/Oxygen Determinator, the surface elements distribution and content of solder powder was detected by X-Ray Photoelectron Spectroscopy (XPS) and the mechanical properties of solder joint were tested by mechanical test enginery. The following results were obtained.(1)After Ce doping, the β-Sn and Ag3Sn phase in solder alloy and power were refined, a small amount of Sn-Ce phase and fine-grain zone area were showed in solder alloy, and the Sn-Ce phase would be gradually broken and reduced with melting time prolonged.(2) The average grain size of β-Sn after Ce doping was only24%of the size without Ce doping in solder joint, but the voids in sold joint increased.(3) The mean grain radius of solder/Cu interfacial IMC was proportional to t1/3of soldering time, the growth of solder/rough Cu interfacial IMC slowed down with Ce doping, but the growth of Solder/smooth Cu interfacial IMC became faster.(4) When powder ratio was at87.5wt%, the Sn-3.0Ag-0.5Cu solder paste had a good printing performance, and Sn-3.0Ag-0.5Cu-0.25Ce solder printed well when powder ratio was at87.5wt.%. The viscosity of solder paste increased when the oxygen content of solder powder rised. (5) The voids mainly existed in the interface, and voids content reduced when the activity of flux increased and solid content lowered. Using hydrochloric acid pretreated solder powder and refined flux, the voids content reduced a lot, and the shear strength of Sn-3.0Ag-0.5Cu solder joint increased from32.37MPa to40.28MPa, the shear strength of Sn-3.0Ag-0.5Cu-0.25Ce solder joint increased from26.46MPa to43.06MPa. |
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